Table 2. Number and proportion of infant deaths that did not link to ONS mortality record and number and proportion of infant deaths that were indicated using HES data only.

	HES birth cohort		ONS Mortality Records
Year of birth	Total infant deaths*	% without a link to ONS mortality record	Total infant deaths	% without a link to HES
1998	2,337	33%	4,357	28%
1999	2,396	24%	4,584	26%
2000	2,269	27%	4,358	27%
2001	1,948	33%	4,320	30%
2002 (introduction of NN4B)	2,104	32%	4,246	29%
2003	2,571	12%	3,967	14%
2004	2,585	10%	3,864	13%
2005	2,602	9%	3,870	11%
2006	2,651	9%	3,931	11%
2007	2,651	10%	3,969	11%
2008	2,668	10%	4,106	12%
2009 (introduction of RON)	2,577	8%	3,985	8%
2010	2,546	6%	3,834	7%
2011	2,444	6%	3,656	7%
2012	2,342	4%	3,509	8%
2013 (correcting postcode extraction error for births in HES)	2,171	5%	3,181	8%
2014	2,075	4%	2,934	8%
2015	2,026	4%	2,924	7%

HES = Hospital Episode Statistics, NN4B = NHS Numbers for Babies (NN4B) ONS = Office for National Statistics, RON = Registration ONline system. Rows marked in grey indicate years when data collection practices have changed.

*Infant deaths were indicated if a linked ONS mortality record was found or if discharge method in hospital record indicated death.